Pattern-forming apparatus using a photomask

ABSTRACT

An apparatus for forming a pattern by using a photomask including both a minute aperture where a main component of a transmitted light is an evanescent light and an aperture where a main component of a transmitted light is a propagating light. The apparatus includes a sample stand for placing a substrate to be processed on which a photoresist with a film thickness equal to or smaller than a width of the minute aperture is formed, a stage for placing the photomask, a light source for generating light for exposure, and a device for controlling a distance between the substrate to be processed and the photomask.

This application is a divisional of U.S. patent application Ser. No.09/781,331, filed Feb. 13, 2001, now U.S. Pat. No. 6,632,593.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a method for forming a pattern using aphotomask in a fine processing process, and a pattern-forming apparatus.

Recently, as a semiconductor memory has become larger in its capacityand a CPU processor has become faster and more integrated, finerphotolithographic techniques have been essentially required. In general,the lower limit of fine processing in a photolithography apparatus isabout the wavelength of the light used. The wavelength of light used ina photolithography apparatus has, therefore, become shorter. Now, a nearultraviolet laser is used, allowing us to conduct fine processing toabout 0.1 μm.

Although photolithography has become finer, there are many problems tobe solved such as a further shorter wavelength of the laser anddevelopment of a lens for such a shorter wavelength band, for fineprocessing of 0.1 μm or less.

On the other hand, there has been proposed an apparatus for fineprocessing utilizing a configuration of a nearfield optical microscope(hereinafter, referred to as an “SNOM”) for achieving fine processing of0.1 μm or less with light. It is a technique in which a photoresist issubjected to a local exposure over a light wavelength limit usingevanescent light leaking out from a fine aperture of 0.1 μm or less.

However, in any lithography apparatus with an SNOM configuration, fineprocessing is conducted like pen writing, using a single processingprobe or several processing probes, so that throughput may not beimproved much.

To solve the above-described problem, there has been suggested atechnique that a photomask having a pattern in which evanescent lightleaks out between shielding films is tightly placed on a photoresist ona substrate and is subjected to exposure, whereby a fine pattern on thephotomask is transferred to the photoresist at one time (Japanese PatentApplication Laid-Open No. 11-145051).

A pattern required in actual lithography is a combination of patternswith various sizes. For example, it is often a combination of patternslarger than an exposure wavelength with small patterns formed byevanescent-light exposure.

Thus, when attempting exposure using a mask where apertures with sizesfor both evanescent-light exposure and propagating-light exposure areprovided on a single matrix, a sensitivity level of the photoresist isdispersed depending on a pattern, so that it is difficult to form auniform pattern because the light intensity of the evanescent light ismuch weaker than that of a the propagating light.

The phenomenon will be detailed with reference to FIGS. 9A to 9C. FIG.9A shows a mask in which an aperture 213 is disposed near an aperture214. In this case, the photoresist is a positive type, and when anegative type photoresist is used, the same result is obtained.

The aperture 213 through which the evanescent light is transmitted as amain exposure component gives a considerably smaller quantity oftransmitted light than that of incident light, depending on its width,shape and its spatial relationship with other patterns.

When the above-described mask is used for exposure while controlling aquantity of the incident light to the mask such that the photoresistreacts by a quantity of the evanescent light, the quantity of light fromthe aperture 214 is so excessive that a photoresist pattern 217 byexposure from the aperture may become larger than the mask pattern andmay cover a portion of a photoresist pattern by the exposure from theminute aperture as shown in FIG. 9B.

On the other hand, the above-described mask is used for exposure whilecontrolling a quantity of the incident light to the mask such that thephotoresist reacts by a quantity of the propagating light from theaperture 214, and the quantity of the evanescent light from the aperture213 is so small that the photoresist may inadequately react, whereby aphotoresist reaction portion by the evanescent light may not be formed,as shown in FIG. 9C.

Similarly, when a photoresist is made thicker, its reaction state maybecome uneven in a photoresist reaction portion 206 by the evanescentlight and in a photoresist reaction portion 207 by the propagatinglight, along the depth direction of a photoresist 203 and along theplane direction of a substrate 204, as shown in FIG. 3A. As a result,only the photoresist reaction portion 207 by the propagating light isformed by development after exposure, as shown in FIG. 3B. Furthermore,the photoresist reaction portion 207 by the propagating light may expandon the substrate 204.

In such a case, patterns may be formed by separate processes; a finepattern is formed by exposure to evanescent light and then a largerpattern is formed by exposure to usual propagating light. However, itmay lead to a higher cost and a lower throughput due to an increase inthe numbers of masks and of process steps.

SUMMARY OF THE INVENTION

In light of the above-described problems, an object of this invention isto provide a method for forming patterns by using a photomask capable offorming uniform large and small patterns, and an apparatus for formingsuch patterns.

The above-described object can be attained by a method for forming afine pattern using a photomask having a combination of a minute aperturewhere the main component of transmitted light is evanescent light and anaperture where the main component of transmitted light is propagatinglight, comprising the steps of: forming a photoresist with a filmthickness of a width or less of the minute aperture on a substrate to beprocessed; and exposing the photoresist by irradiating it with light forexposure.

The object of this invention can also be achieved by an apparatus forforming patterns on a substrate to be processed, the apparatuscomprising:

a sample stand for placing the substrate to be processed having aphotoresist with a thickness of an exposure wavelength or less formedthereon;

a stage for placing a photomask having a shielding film formed on aphotomask substrate, the shielding film having the combination of anaperture having the first width where the main component of lighttransmitted through the aperture is evanescent light and anotheraperture having the second width where the main component of lighttransmitted through the other aperture is propagating light;

a light source for exposure which generates light for exposure; and

means for controlling a distance between the substrate to be processedand the photomask.

These details will be later described in Examples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view for showing an apparatus for forming patternsaccording to this invention.

FIGS. 2A, 2B, 2C and 2D are schematic views for showing a method forforming patterns according to this invention.

FIGS. 3A and 3B are schematic views for showing an exposure state in thecase of a thick photoresist in a conventional example.

FIGS. 4A and 4B are schematic views for showing an exposure state and apattern after exposure according to this invention.

FIG. 5 is a flow chart of a process for forming patterns according tothis invention.

FIGS. 6A, 6B, 6C, 6D and 6E are schematic views for showing a photomaskand a method for forming patterns in Example 1 according to thisinventiion.

FIGS. 7A, 7B, 7C, 7D and 7E are schematic views for showing a method forforming patterns by using two buffer layers in Example 2 according tothis invention.

FIGS. 8A, 8B, 8C and 8D are schematic views for showing a method forforming patterns by using one buffer layer in Example 3 according tothis invention.

FIGS. 9A, 9B and 9C are schematic views for showing a mask pattern andphotoresist patterns formed by different exposure quantities,respectively.

FIGS. 10A and 10B are schematic views for showing a difference between amask pattern and a photoresist pattern after exposure.

FIGS. 11A and 11B are schematic views for showing a mask pattern whereminute apertures are periodically aligned in Example 5 and a photoresistpattern according to this invention.

FIGS. 12A, 12B, 12C and 12D are schematic views for showing a method forforming patterns by using a layer absorbing light for exposure as thefirst layer in Example 6 according to this invention.

FIGS. 13A, 13B, 13C and 13D are schematic views for showing an exposurestate of using an elastic mask in Example 7 according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of this invention will be described in detail with referenceto the drawings.

FIG. 1 shows an apparatus for forming patterns according to thisinvention. In FIG. 1, numeral 103 indicates a sample stand for placing asubstrate (sample) 107 to be processed, numeral 102 indicates a stagefor placing a mask 106 for exposure, and numeral 101 indicates a lightsource and numeral 105 indicates a light for exposure. Light forexposure is, of course, adjusted to cover over the whole exposureregion, and, more suitably, may be adjusted to enter perpendicularly toa film for improving energy efficiency. In FIG. 1, numeral 104 indicatesdistance-controlling means for controlling a distance between thephotoresist and the photomask 106.

A pattern-forming method using a photomask in this invention will bedescribed with reference to FIGS. 2A to 2D.

A photomask 106 has a transfer pattern of a shielding film 202 whichshields light for exposure, in one side of a glass substrate 201 throughwhich light for exposure is transmitted. The transfer pattern has both aminute aperture 213 having a size such that evanescent light leaks outtherethrough as light for exposure and an aperture 214 having a sizesuch that propagating light is transmitted therethrough. The minuteapertures 213 and the aperture 214 do not necessarily have the samewidth, respectively.

The minute aperture 213 having a size such that evanescent light leaksout therethrough has a width shorter than a wavelength of light forexposure. There are no restrictions in length to a minute aperturepattern in the longitudinal direction, and the pattern may be freelyselected. The aperture having a size such that the propagating light maybe transmitted therethrough has a width longer than the wavelength oflight for exposure.

A material for the shielding film is preferably a metal such as Au or Albecause it does not transmit light for exposure and it may be readilyprocessed to give a fine pattern. Chemically stable Cr is morepreferable because it is hard enough to be resistant to scratches andbecause, when a photomask is pushed against a photoresist, residueadhering to the photomask can be washed out with a washing liquidcontaining an oxidizing agent.

The shielding film has a thickness adequate to prevent the transmittedlight through the shielding film from exposing the photoresist.Effective pattern formation can be achieved when a thickness L of theshielding film meets the following equation:L>ln A·λ/2πk(A=P·t/Eth)  (1)

wherein K is an extinction coefficient of a material used for theshielding film, Eth is a photoresist sensitivity, λ is an exposurewavelength, t is an exposure time, P is an exposure quantity and inrepresents a natural logarithm. The thickness is, however, preferablythe minimum value meeting equation (1) because a thinner film canfacilitate pattern formation and improve dimensional accuracy.

A pattern-forming method using a shielding film on a photomask may beconducted according to a conventional process employing layerprocessing, EB (Electron Beam) or X-rays. A method generally andfrequently used for forming patterns on a photomask is an EB drawingprocess. Alternatively, the pattern formation can be conducted by usingan SPM (Scanning Probe Microscope).

In processing using, for example, an AFM (Atomic Force Microscope),among SPMs, an aperture may be formed on a photomask by scanning acantilever while the cantilever is pushed against the surface of theshielding film on the photomask to shave the surface. Patterns withvarious aperture widths may be formed by varying pressure applied to thesurface, a scanning direction and a shape of the tip of the cantileverused.

Further, it is necessary that a thickness of the photoresist formed onthe substrate to be processed is not larger than the width of a minuteaperture where the main component of transmitted light is evanescentlight, in the light of a difference in an intensity between theevanescent light and the propagating light. The reason will be describedin detail.

In a minute aperture where the main component of transmitted light isevanescent light, the quantity of that transmitted light is considerablysmaller than that of the incident light although it depends on the shapeof the minute aperture. Thus, it is difficult to adjust a light-quantityratio between the evanescent light and the propagating light whenconducting exposure using both lights at the same time. When a filmthickness is equal to or less than the width of the minute aperture,however, this prevents the propagating light from eroding a patternformed with the evanescent light as shown in FIG. 9B because a patternformed by the propagating light does not expand in the film planedirection over a distance corresponding to the film thickness of thephotoresist. Thus, a film thickness of the photoresist equal to or lessthan the width of the minute aperture can prevent a pattern fromextending to an adjacent pattern.

Thus, a photoresist with a thickness equal to or less than the width ofthe minute aperture may be used to minimize extension of a photoresistreaction portion 219 on a substrate 204 by the propagating light asshown in FIG. 4A and may allow a photoresist reaction portion 218 by theevanescent light to reach the substrate 204 so that the transfer patternon the photomask can be exactly formed on the substrate 204 even whenthere are apertures with various sizes on the photomask (FIG. 4B).

The evanescent light has a light quantity less than that of thepropagating light, but its pattern may extend, although by only a smallamount, along a film plane direction. Therefore, it is similarlyeffective to adjust a thickness of the photoresist to be a value equalto or less than the width of the smallest pattern formed on thesubstrate to be actually processed in the light of such an extension.

The evanescent light 210 has a light quantity considerably smaller thanthat of the incident light for exposure 205 to the photomask, i.e., theratio of the former to the latter is about 1×10⁻⁷:1 although it dependson the shape of the minute aperture. For exposure of the photoresistreaching the substrate by the evanescent light, it is preferable thatthe thickness of the photoresist is 100 nm or less and the filmthickness ranges 0<h≦100, where h (nm) is a film thickness.

Correction of a mask pattern will be described.

When a size difference between a pattern after development and anaperture 214 on the photomask due to an extension of the photoresistreaction portion 219 on the substrate 204 is significant in exposure bythe propagating light, the width of the aperture may be adjusted to besmaller than a designed dimension.

Specifically, it is preferable to adjust the size of the aperture when aprecision error required for a distance between an aperture 214 and aminute aperture 213 or a pattern size after exposure by an aperture 214is 1 μm or less, although it may depend on a photoresist or processused.

In a process conducted after pattern formation described above, it ispreferable to form a buffer layer between the substrate and thephotoresist when an aspect ratio in a pattern formed on the substrate istoo small to satisfactorily conduct a process such as etching anddeposition. For example, there may be formed a multilayer structurecomprising a dry-etching resistant layer, an oxygen-RIE (Reactive IonEtching) resistant layer and a thin photoresist layer for imageformation in sequence from the side of the substrate, and then a patternformed in the thin photoresist layer for image formation is transferredto another thick layer to form a pattern with a higher aspect ratio.

A material for the photoresist 203 may be selected from those used in ausual semiconductor process. A light wavelength for exposing thesematerials ranges within about 200 to 500 nm. In particular, aphotoresist corresponding to a g-ray or an i-ray within a range of 350to 450 nm may be selected to improve process flexibility and to reducecost because of its diversity and relatively lower cost.

It is preferable to apply an antireflection film on the substrate when apattern shape formed along a direction perpendicular to the substrate isdistorted due to mutual interference between light for exposurereflected on the substrate and light for exposure entering thesubstrate.

When there is formed a buffer layer between the photoresist and thesubstrate to be processed, it is preferable that the buffer layer bemade of a material exhibiting a lower transmittance to light forexposure in order to prevent pattern extension due to going around oflight for exposure from the lower layer of the photoresist.

The light used for the exposure must have a wavelength such that thephotoresist 203 used can be exposed. For example, when the abovephotoresist corresponding to the g-ray or i-ray is selected as thephotoresist 203, exposure may be conducted using a HeCd laser (lightwavelength: 325 nm, 442 nm), a GaN blue semiconductor laser (410 nm), asecond harmonic generation (SHG) laser or third harmonic generation(THG) laser in an IR laser or a mercury lamp (g-ray: 436 nm, i-ray: 365nm).

A process for forming patterns according to this invention will bedescribed with reference to FIGS. 2A to 2D.

The photoresist 203 is applied on the surface of the substrate 204 to athickness of 100 nm or less. It is preferably as thin as possible;specifically, 0<h≦100, where h is a film thickness (nm).

Then, as shown in FIG. 2A, the photoresist 203 is made close to the sideof the photomask made of a glass substrate 201 on which a shielding film202 is formed until the shielding film 202 evenly contacts with thephotoresist 203 (FIG. 2B).

Contacting the shielding film on the photomask with the photoresist maybe conducted by fixing one of the photomask and the photoresist and thenmaking the other not fixed close to the fixed one by using, for example,a micrometer; by applying pressure to the other not fixed to the one byutilizing a solid, liquid or gas; or by evacuating the space betweenboth by using, for example, a vacuum pump.

When an elastic film mask is used, the space between the mask and thephotoresist can be evacuated to bend the mask so that the whole surfaceof the mask may be closely in contact with the surface of thephotoresist.

As shown in FIG. 2C, the photoresist 203 is exposed by irradiation oflight 205 for exposure from the side having no shielding film 202 of theglass substrate 201.

The photoresist may be a positive or negative type one. FIGS. 2A to 2Dshow a state of using a negative type photoresist.

The negative type photoresist 203 under the portion having no shieldingfilm 202 on the photomask becomes development-resistant as a photoresistreaction portion 211. Removing the photomask and then development canprovide a pattern consisting of photoresists with various widthsreflecting the pattern of the shielding film 202 on the photomask, onthe substrate 204 (FIG. 2D).

After exposure by the propagating light and the evanescent light asdescribed above, the substrate 204 may be processed as usual. Forexample, after developing the photoresist, etching is conducted, on thesubstrate 204, to form a pattern corresponding to the pattern formed inthe photoresist on the substrate.

FIG. 5 shows a flow chart of the formation process.

As described above, the method of this invention can provide uniformpatterns with various sizes from a minute pattern smaller than adiffraction limit of light to a pattern which can be formed by usualphotolithography, by using one sheet of photomask, thereby resulting inimprovement of throughput in a photolithography step.

This invention will be more specifically described with reference toExamples. These examples are the most preferred embodiments of thisinvention, but do not limit this invention at all.

EXAMPLE 1

FIGS. 6A to 6E show a method for forming a pattern according to thisexample.

On a glass plate 650 as a photo substrate, an Al thin film 651 is formedto a thickness of 36 nm as a shielding film by sputtering. As shown inFIG. 6A, while pushing the needle tip of a cantilever 652 for AFM withan elastic constant of 45 N/m against the thin film at a pressure ofabout 1×10⁻⁵N, the Al thin film 651 is scanned with the cantilever toform a minute aperture 653 with an opening width of about 100 nm (FIG.6B). The cantilever 652 AFM is moved several times while pushing itsneedle tip against a Ti film to blunt the needle tip. Then, whilepushing the blunted needle tip against the Al thin film 651 at apressure of about 5×10⁻⁵N, the Al thin film 651 is scanned with thecantilever as described above to form an aperture 654 with an openingwidth of 1 μm.

An antireflection film is formed on an Si substrate 601, and then apositive type photoresist 602 corresponding to a g-ray is formed thereonto a thickness of 100 nm by using a spin coater. Then, the photoresist602 is pre-baked.

The positive type photoresist 602 may be exposed using a mask aligner(Model MA-10, manufactured by Mikasa Company). First, as shown in FIG.6C, the Al thin film 651 is moved toward the positive type photoresist602. After contacting the Al thin film 651 with the positive typephotoresist 602, the positive type photoresist 602 is irradiated withlight 609 (10 mW) for exposure from a mercury lamp for 3 seconds toexpose the photoresist with the evanescent light 610 leaking from theminute aperture 653 and the propagating light 615 through the aperture654, thereby forming a photoresist reaction portion 611 which can bedissolved in a developing solution within the positive type photoresist602 (FIG. 6D). After exposure, the Al thin film 651 is removed from thepositive type photoresist 602. Then, the positive type photoresist 602is developed and post-baked.

Thus, both the fine pattern of 100 nm and the pattern of 1 μm aretransferred on the Si substrate 601 by a single exposure (FIG. 6E).

EXAMPLE 2

FIGS. 7A to 7E show a method for forming a pattern in this example usingtwo buffer layers and a photoresist layer. FIG. 7A shows a photomask andan object to be exposed. A Cr thin film is vapor-deposited to athickness of 60 nm on one side of a glass substrate 705. Then, toprocess this Cr thin film by using an EB (Electron Beam) drawingapparatus, a photomask having a shielding film 706 as a pattern to betransferred is formed. Here, on the photomask, there are both the minuteaperture 753 having a size where the evanescent light leaks as the maincomponent of transmitted light and the aperture 754 through which thepropagating light is transmitted.

On an Si substrate 701 on which a shielding film is to be contacted, apositive type photoresist is formed to a thickness of 500 nm by using aspin coater, and then the photoresist is heated at 200° C. for 30minutes to form the first layer 702. On the first layer 702, an organicsolvent solution of SOG (Spin On Glass) is formed and the solution isheated to form an oxidized Si film with a thickness of 100 nm as thesecond layer 703. On the second layer 703, a negative type photoresistis formed to a thickness of 50 nm for forming an image for the thirdlayer 704 and it is then pre-baked at 110° C. for 10 minutes.

The Si substrate 701 is placed on a sample stand in a mask aligner andthe sample stand is moved toward the photomask by using a micrometer.After bringing the photoresist as the third layer 704 into contact withthe shielding film 706 of the Cr thin film on the photomask, the thirdlayer 704 is exposed by the evanescent light 708 and the propagatinglight 710 from light 707 for exposure to transfer the pattern of theshielding film 706 to the third layer 704 as a photoresist reactionportion 709 (FIG. 7B).

The photomask is removed from the photoresist of the third layer 704.Then, the photoresist of the third layer 704 is developed andpost-baked. Thus, the pattern to be transferred on the photomask istransferred to the third layer 704 (FIG. 7C). Then, the second layer 703is patterned by dry etching using the pattern transferred to the thirdlayer 704 as a mask (FIG. 7D). By using the pattern in the second layer703 thus formed as a mask, the first layer 702 is processed with oxygenRIE (FIG. 7E).

Thus, the patterns with various sizes to be transferred are transferredon the Si substrate 701 with higher contrast. Since an aspect ratio ofthe photoresist on the Si substrate 701 is high, a pattern by which asubsequent device process can be readily conducted can be formed.

EXAMPLE 3

FIGS. 8A to 8D show a method for forming a pattern in this example byusing one buffer layer and a photoresist layer. FIG. 8A shows aphotomask and an object to be exposed. On one side of a glass substrate805, a Cr thin film is vapor-deposited to a thickness of 80 nm. And, toprocess this Cr thin film by using an EB (Electron Beam) drawingapparatus, a photomask having a shielding film 806 as a pattern to betransferred is formed. Here, on the photomask, there are various sizesof apertures, i.e., those with a size where the evanescent light leaksas the main component of transmitted light and those through which thepropagating light is transmitted.

On an Si substrate 801 on which a shielding film has been formed, apositive type photoresist is formed to a thickness of 400 nm by using aspin coater, and then the photoresist is heated at 200° C. for 30minutes to form the first layer 802. On the first layer 802, anSi-containing negative type photoresist is formed to a thickness of 80nm and the layer is pre-baked to form the second layer 803.

The Si substrate 801 on which the two-layer photoresist has been appliedis moved toward the shielding film 806 on the photomask and finally, thesecond layer 803 is contacted with the shielding film 806 of the Cr thinfilm on the photomask.

Then, the second layer 803 is exposed by the evanescent light and thepropagating light from light 807 for exposure to transfer the pattern ofthe shielding film 806 to the second layer 803 as a photoresist reactionportion 809 (FIG. 8B). The photomask is removed from the photoresist.Then, the photoresist is developed and post-baked. Thus, the pattern tobe transferred and the photomask is transferred to the second layer 803(FIG. 8C).

While using the pattern transferred to the second layer as a mask, thefirst layer is processed with oxygen RIE (FIG. 8D). By using oxygen RIEin processing, Si contained in the second layer is oxidized to improveoxygen-RIE sensitivity.

Thus, the original patterns to be transferred having various sizes onthe photomask are transferred onto the substrate 801 with a highercontrast by a single exposure. Throughput is improved because ofreduction of the number of photoresist formations to two and the numberof pattern transfers.

EXAMPLE 4

There will be described a case in which an aperture is very close to aminute aperture or in which an acceptable precision error is 1 μm orless for a pattern after exposure.

FIG. 10A shows a mask pattern while FIG. 10B shows a photoresist patternformed by developing a photoresist after exposure using the mask shownin FIG. 10A. In FIG. 10A, the contour 222 of a pattern with a desiredsize is indicated by a dotted line.

Since a light quantity from a minute aperture 213 with a pattern widthof 100 nm is considerably lower than a light quantity from an aperture214, exposure adjusted for the minute aperture 213 may make aphotoresist pattern 217 by exposure from the aperture 222 larger thanthe aperture 214.

A positive type Si-containing photoresist is patterned using a maskaligner. In this case, a minute aperture pattern for a mask patternwidth of 100 nm as an exposure pattern cannot be formed in thephotoresist under the conditions of an exposure time of 30 seconds and adevelopment time of 5 seconds. When the exposure time was 100 seconds, aphotoresist pattern 216 by exposure from the minute aperture 213 couldbe formed.

Meanwhile, the photoresist pattern 217 by exposure from the aperture 214was expanded by about 10% when an exposure time was increased. Thus,exposure was conducted to an aperture pattern with a size smaller thanthe desired pattern size 222 by 10% so that desired photoresist patternswith various sizes could be formed.

EXAMPLE 5

In this example, there will be described a pattern where minuteapertures are periodically aligned. FIG. 11A shows a mask having bothperiodically aligned minute apertures 913 through which the evanescentlight leaks and an aperture 214 through which the propagating light istransmitted.

In such a structure where the minute apertures are periodically alignedwith a pitch of an exposure wavelength or less, a transmissionefficiency is higher than an isolated minute aperture pattern. In aperiodic structure having five apertures with a pattern width of 80 nmand a pitch of 200 nm, an about 15-fold quantity of light compared withan isolated minute aperture is transmitted through the mask pattern perone aperture.

Thus, exposure was conducted in an exposure light quantity such that theperiodic fine photoresist pattern 916 was formed by exposure with theperiodic minute aperture 913, whereby pattern expansion of thephotoresist pattern 217 due to exposure from the aperture 214 could beminimized.

EXAMPLE 6

In this example, a buffer layer for absorbing light for exposure isformed under the photoresist layer. FIG. 12A shows a photomask and aphotoresist used in this example. On one side of a mask substrate 905, aCr thin film is deposited to a thickness of 80 nm, as a shielding film806. An original pattern to be transferred is formed into this shieldingfilm by using an EB (Electron Beam) drawing apparatus. Here, on thephotomask, there are apertures having various sizes, i.e., an aperturehaving a size with a width of 80 nm or more where the evanescent lightleaks as the main component of transmitted light and an aperture havinga size where the propagating light is transmitted.

On an Si substrate 801, a positive type photoresist corresponding to ag-ray is formed to a thickness of 400 nm by using a spin coater. It isthen heated at 200° C. for 30 minutes to form the first layer 822. Onthe first layer 822, an Si-containing positive type photoresistcorresponding to KrF is formed to a thickness of 80 nm and it waspre-baked to form the second layer 803.

The Si substrate 801 on which the two-layer photoresist has been formedis moved toward the shielding film 806 on the photomask and finally, thephotoresist of the second layer 803 is contacted with the shielding film806 of the Cr thin film on the photomask.

Then, the second layer 803 is exposed by the evanescent light and thepropagating light 807 from a KrF light source for exposure to transferthe pattern of the shielding film 806 to the second layer 803 as aphotoresist reaction portion 809 (FIG. 12B).

The photoresist as the first layer may absorb light for exposure toprevent reflection and expansion.

The photomask is removed from the photoresist. Then, the photoresist isdeveloped and post-baked. Thus, the original pattern to be transferredon the photomask is transferred to the second layer 803 (FIG. 12C).

While using the pattern transferred to the second layer as a mask, thefirst layer is processed with oxygen RIE (FIG. 12D). By using oxygen RIEin processing, Si contained in the second layer is oxidized to improveoxygen-RIE resistivity.

As described above, a light quantity adjusted for the minute aperturecould be used to simultaneously form patterns by exposure from theminute aperture and the aperture. Furthermore, the first layer was alayer with a higher absorbance of an exposure wavelength, which couldminimize pattern expansion in a direction along the substrate plane byexposure from the aperture.

EXAMPLE 7

In this example, there will be described an exposure method using anelastic material for a photomask. FIG. 13A shows a photomask and aphotoresist used in this example. On an Si substrate as a mask support902, SiN as a mask material 901 is vapor-deposited to 1 μm. On thisside, a Cr thin film is vapor-deposited to a thickness of 50 nm. Toprocess this Cr thin film by using an FIB (Focused Ion Beam) drawingapparatus, an elastic photomask having a shielding film 806 as a patternto be transferred is formed. On the photomask, there are apertureshaving various sizes, i.e., a minute aperture 753 having a size with awidth of 80 nm where the evanescent light leaks as the main component oftransmitted light and an aperture 754 having a size where thepropagating light is transmitted.

On an Si substrate 801 on which a shielding film has been applied, apositive type photoresist is applied to a thickness of 400 nm by using aspin coater. It is then heated at 200° C. for 30 minutes to form thefirst layer 802. On the first layer 802, an Si-containing positive typephotoresist is applied to a thickness of 80 nm and it was pre-baked toform the second layer 803.

The Si substrate 801 on which the photoresist of a two-layer structurehas been applied is moved toward the shielding film 806 on thephotomask. Furthermore, the air between the photomask and the secondlayer photoresist 803 is evacuated with a pump to bend the elasticphotomask due to the atmospheric pressure and evenly contact the secondlayer photoresist 806 with the thin film photomask over a large area(FIG. 13B).

Then, the second layer 803 is exposed by the evanescent light and thepropagating light from light for exposure 807 to transfer the pattern ofthe shielding film 806 to the second layer 803 as a photoresist reactionportion 809 (FIG. 13C). The photomask is removed from the photoresist.Then, the photoresist is developed and post-baked. Thus, the originalpattern to be transferred on the photomask is transferred to the secondlayer 803. While using the pattern transferred to the second layer as amask, the first layer is processed with oxygen RIE.

Thus, the photoresist is more closely contacted with the photomask byusing the thin film photomask. In addition, oxygen RIE may be used inprocessing to oxidize Si contained in the second layer, thereby leadingto improvement in oxygen-RIE resistance.

As described above, according to this invention, a photoresist which isformed with a thickness equal to or smaller than a minute aperture sizeon a substrate is exposed by using a photomask having a minute aperturepattern where the evanescent light is the main component of light forexposure of the photoresist and an aperture pattern where thepropagating light is the main component of light for exposure of thephotoresist, so that photoresist patterns with various sizes can beformed on the substrate by a single exposure.

1. An apparatus for forming a pattern, said apparatus comprising: aphotomask for light exposure provided with both a first aperture havinga minute width where a main component of transmitted light is evanescentlight and a second aperture having a larger width than that of saidfirst aperture where a main component of transmitted light ispropagating light; a sample stand for placing a substrate to beprocessed on which a photoresist with a film thickness equal to orsmaller than a width of the first aperture is formed; a stage forplacing the photomask; a light source for generating light for exposure;and means for controlling a distance between the substrate to beprocessed and the photomask, wherein the width of said second apertureis smaller than a designed dimension of said photomask and the width ofsaid second aperture is longer than a wavelength of light for exposure.2. The apparatus according to claim 1, wherein the photomask comprisesan elastic material as a mask material.
 3. The apparatus according toclaim 1, wherein the width of said first aperture is shorter than awavelength of light for exposure.
 4. An apparatus for forming a pattern,said apparatus comprising: a photomask for light exposure provided withboth a first aperture having a minute width in which a main component oftransmitted light is evanescent light and a second aperture having alarger width than that of the first aperture in which a main componentof transmitted light is propagating light; a sample stand for placing asubstrate to be processed on which a photoresist is formed; a stage forplacing the photomask; a light source for generating light for exposure;and means for controlling a distance between the substrate to beprocessed and the photomask, wherein the size of the second aperture isless than that of a pattern to be formed in the photoresist bydeveloping the photoresist after exposure using the photomask, and thewidth of the second aperture is longer than a wavelength of light forexposure.